Loading coil and method of construction



Dec. 22, 1925- 1,566,802

1. L. MILTON LOADING COIL AND METHOD OF CONSTRUCTION Filed May 1, 1923 Patented Dec.

UNETEE) EATENT OFFER.

IVAN L. MILTON, OF WESTERN SPRING-S, ILLINOIS, ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NET/V YORK.

LOADING COIL AND METHOD OF CONSTRUCTION.

Application filed May 1,

To all "whom it may concern:

, Be it known that I, IVAN L. MILTON, a

citizen .of the United States, residing at WVestern Springs, in the county of Cook, State of Illinois,,have invented certain new and useful Improvements in Loading Coils and Methods of Construction, of which the following is a full, clear, concise, and exact description.

This invention relates to the loading of telephone systems, and more particularly to means and methods for reducing or preventing inductive interference or cross-talk between the circuits of systems in which the same loading unit is used to load more than .one circuit, as may be done in the case of two physical circuits and their derived phantom circuit.

In order that the cross-talk arising in such a loading unit shall be a minimum, the mutual inductances between each of the line windings in one physical circuit and those in the other physical circuit should be equal or at least very nearly so. For, if one line winding is more susceptible than the other line winding of the same physical circuit to the variations of flux accompanying speech currents flowing in the windings of the other physical circuit, cross-talk currents will be set up in .the first circuit due to the inequality of electromotve forces induced in its two windings and their consequent failure to balance each other; in like manner inequalities of mutual inductance between the windings may cause cross-talk between either of the physical circuits and the derived phantom circuit.

Inequalities of mutual inductance may arise, for instance, from lack of homogeneity as to permeability of the core of the loading unit, such as may be caused in cores made up of laminations or the like by differences in the lan'iinations or the closeness of their contact. The effects of such inequalities, though perhaps negligible in shortlines in which low voltagesiand small currents are encountered, become accentuated to a harmful degree under the high pressures occurring in long lines, especially in systems in which amplifying repeaters are employed.

It is the object of this invention to provide a loading unit in which the mutual inductances between the several windings are so closely "balanced as to prevent appreciable 1923. Serial No. 635,869.

crosstalk under severe service conditions; a further object is to afford a method for producing such a condition of balance.

Briefly, the objects of this invention are obtained by connecting in circuit with one of the main windings for each side circuit a supplementary winding located on the section of the core carrying the mate winding for that side circuit. These windings are adjusted to produce by mutual inductance between the windings an E. M. F. having the proper amplitude and phase to overcome the cross-talk diificulties encountered.

Referring to the drawings, Fig. 1 represents this invention applied to a loading unit for simultaneously loading two physical circuits and their derived circuit, and Fig. 2 illustrates more in detail the type of core used in the loading unit shown in Fig. 1.

Referring to Fig. 1, A indicates one side circuit comprising the line conductors 5 and G, B represents the other side circuit comprising the line conductors 7 and 8 and C represents a phantom circuit derived from the two physical circuits in a well-known manner. The loading unit illustrated in this figure has four semi-annular core sections 9, 10, 11 and 12 joined together in such a manner as to form in effect two complete rings intersecting at right angles on a common diameter. The two rings may he of any suitable magnetic material but; are preferably formed of finely divided iron with the individual particles insulated from one another, this material being molded under high pressure into the required form.

The core sections 9 to 12 are provided respectively with the main windings 13, 1a, 15 and 16.

Due to the relative positions of the four windings 13 to 16, there will be a mutual inductance effect between each winding and each of the remaining windings. In the general case, it will be found that these n'uitual inductances between the four main windings will not neutralize each other but will give rise to a resultant F. M. F. in the transmission circuit which will cause cross-talk be tween the two side circuits or between the phantom circuit and one of the sidecircuits. Cross-talk is, of course, objectionable in a high quality circuit and the arrangement of this invention has therefore been provided to eliminate this effect due to any inequality of mutual inductance betweenthe respective windings of the loading coil un'it.;

I bThe manner in which cross-talk is elimifcilcuit C n h du o the mut l i d cr,

hated in accordance with this invention will beg-understood 1f we assume that phantom circ nit currents are'flowing III the phantom tance between Winding 13 f side'circ'uitA i and windings'l5 and 16 01": sidecircuit B an electro'motive force is producedin winding 13' giving riseto a current in the direction indicated byari'ow 17 Thelmutu'al inductance between Winding l w m e Ofth windings 1 and ;-"16,wi 1l, be assumed to, give 'riseto an electrioinotive 'force in winding 14,

producing a current flowing in thedirecti0n ,1 indicated by arrow is whichnis in the 0pcrds s t alic In ac rdance, with; this invention, ,the ele'tiflomotivejforces" introduced} in the above I I T QI t'mvindi 'g l a 1 y b eqn'aliZ'edan'd therefore annulled'iby connectingv in series: with Wilidingli: a-Qsupplementgal 5y winding 19 K the few, 'tiirns, Ioit ,whieh are .wound 7 ion the v core section, {surrounded by windinglg rovided that the electroinotive 7 force introduced iii.;,w v;i;nd11ig 14 is of the {lesser inagnitude, w inding 19 should be so us'teda stto produce an electro'inoti e f e inl i id g Beef-Lin P op r" ii ,mdeand bhaselto neutraliiz'e the e1ec.tromo due totheinutual indiictance H s with'the windings" l5 and 1645.1 the side circuit The procedure to be employed in testing and adjnetin'g: \iallues ojf the windin'g 19.,is sir nilar to the procedure ontline'dtin detail in thell patent to lshackelton No.

1, 3345,3221 o;f "Ma.rch 23,1 192o, V r

In case the electroinotive force in Winding ladue to this mutualoinductance is smaller than that induced in winding 13 winding 19 n e n t be. pley u wCQ I P Iidi g ;ing,,13 and wound around core'section amp e, wii'r :2 i e 3 s i jj subpleinentary winding in series With wind- Thfl ei fi b it l y be i h e-lf y tr a ed by o ieti 'g 1 v lij l i th 7-.- (i l Of 1 6 wi dings s o 1'6 supplementary W ding wound on. that hart of the core surrounded bathe onetim er d f asr ticuIar utility'when air v The HbOVQdQSCI'ibGQI HIGthQd Of reducing. cross-talk by 'niacinp: in, series; jwith one winding a few turns woundaround the core surrounded by its mate Winding is of pargaps ale-'empldyedin the Gimba'l cor e to separate the c'or'e branches in the manner well knownin the art and as shown,' for example, in Fig; 2 in which air ga-ps 25 and 26am inserted in the Gimbai core atthe junction of the two annular rings and at right angles to each other toproyidef the desired separation between "the-bore branches i9 10, 11 and, This isrpi'ob ably duelto the. nntual inductances in such .a case being'srnall Compared to the selfinductances It-is to be understood that the fo'rniof this invention; described above is notgthe only e nbodi nent or this invention and; that inedifications thereof may be made Without,'de *?5 partingfron the spirit of intention, as defined in the appended cl a r n e. 7 1 Theinvention clai nedfli s T e le hed .of-co P ensatin anti- 'ent permeability between sectionsofthe cor? of an inductioncoil whichcarr y'the main -findings for the physicalfcirc iits in which the, coil 7 is. to be connected; ,nio untedl on V difierentsections, which inethod comprises eonnectingto one inain winding a;supplenien. iary winding mountedwon that section ofthe core which carries (the '1na tewinding for a ne a m n din \e lP P Qn n the nu'n beiyand direction the turns of said supplementary winding to obtain an in.-

theinduction coil. y l a T v m thq q m ense ne io differences of .mutual;inductance between the windings, ofa loading coil adapted for. use

s ith two physicallcircuits a; delr iyed phantom cir cuit, the loading coil having a CQI'e of aplurality of branches on which the main windings for lthetwol physicalcircuits 7 are tdistributed, which Inethod com i es in;- cluding in series with one winding of each physical; cii'cuit a supplementary winding n'iounted on the branch the,pr surrounded bythe nate winding ofsai d one winding and adjusting by trial the. number andjdirection of turns of said auxiliary 'windings to-obtain a inutuai inductance balaii'ce ber tween the various windings of the loading coih both for side cii'euit working and for: phantom circuit working; V 3-; Th th le e iii nse ng for dif ierences of inutual induetance between the windings of a loading coil adapted use with two physical circui ts andQa der red arranged 1 t teb a i s with h eiumn '1ii.ai1i wiiaam or each physical 5ft ductance balance. between the windings of V nit a supplementary Winding mounted on the same branch of the core as the mate Winding for said one Winding and adjusting by trial said supplementary windings so as to produce equal mutual inductances between each of said one Winding and each of the two main windings of the second physical circuit.

i; A loading coil comprising a core of a plurality of sections, tWo main windings on different sections of said core for each physical circuit to be loaded by said loading coil, and a supplementary Winding the turns of which are proportioned in number and direction to give an inductance balance be tween the windings 1n series With one main winding of each physical circuit and mounted on the core section surrounded by the mate winding of said one main Winding.

5. A loading coil comprising a core of four semi-annular core sections joined together to form in effect two complete toroids intersecting at right angles on a common diameter, gaps of high specific resistances at the intersecting points for separating the four semi-annular core sections, a main winding on each of said core section and a supplementary winding connected in series with the winding on one of said core sections and mounted on the other hall of the toroid formed thereby, and a supplementary winding in series With the main Winding 011 a third of said core sections and mounted on the fourth of said core sections.

In Witness whereof, I hereunto subscribe my name this 26 day of April, A. D. 1923.

IVAN L. MILTON. 

